For panels used in building and construction applications, flame retardant materials are desirable to protect against the spread of fire. Flame retardant panels are often used to cover the external as well as internal surfaces of buildings and usually have a “sandwich” structure, the two external layers being made of metal and the intermediate layer of a flame retardant composition as described in the next paragraph below.
Important characteristics for flame retardant compositions for construction panels are high flame retardancy, good heat performance and good mechanical properties. Today, typical flame retardant compositions suitable for the manufacture of building panels are based on blends of polyethylene (PE) and/or ethylene vinyl acetate (EVA) with up to about 75 wt-% of a flame retardant additive such as aluminum trihydrate (ATH) and/or magnesium hydroxide. With the aim of meeting high demanding government test standards, such as for example DIN 4102 Class A2, many improvements have been achieved to improve the flame retardancy of the compositions by highly increasing the amount of flame retardant additives (up to about 90 wt-%). While the incorporation of such high amounts of flame retardant additives confers to the composition a high flame retardancy, such compositions have several drawbacks. The incorporation of such high amounts of flame retardant additives leads not only to the deterioration of the mechanical properties of the thermoplastic polymer (the plastic becomes e.g. brittle, losing elasticity in comparison with the starting polymer, which is a disadvantage for many applications) but also leads to difficulties in the manufacture of the composite panels. With increasing the amount of the flame retardant additives, the thermoplastic composition has poor processing characteristics and thus cannot be processed by conventional means such as for example extrusion or calendering. With such elevated amount of flame retardant additives in the thermoplastic compositions, flame retardant composite panels are manufactured by bonding together the aluminum sheets and the thermoplastic composition using an adhesive polymer and a process such as a flat bed lamination with the use of appropriate heat and pressure conditions.
On the other hand, there is also a general desire in building and construction applications to be cost efficient. Flame retardant agents such as ATH are expensive so that typical flame retardant compositions which include high amounts of these compounds may become expensive. The elevated costs of the flame retardant additives such as ATH or magnesium hydroxide as well as the complexity and investment cost of the needed manufacturing processes render the production of these composite panels unattractive.
There is thus a need for flame retardant panels that exhibit high flame retardancy and which can be manufactured at reasonable costs with conventional processes.